You must have landline to use CapTel. With WebCapTel, you don't. All you need is a VoIP (Voice over Internet Protocol) phone or cell phone and your computer to make WebCapTel calls. As an addition to CapTel, you'll have to fill out a paperwork for CapTel phone. Unless you have a 2-line CapTel service (that is, your caller can dial your phone number without dialing a 1-800 number first), with a 1-line CapTel or WebCapTel, they'll have to have someone dial a 1-800 phone # before they dial your phone number. A drawback with WebCapTel is that you have to stay logged on at all times and enable "Wait for Call" feature as to have a caller call you, so you can get captions.
I tried out SprintCapTel.com and it worked (even with my Sprint Samsung Ace, but I have to use my cell phone specifically for voice since I can't talk/surf at the same time with my Samsung Ace). It just takes some time for captions to show up (even with CapTel).